1. Field of the Invention
The present invention relates to a substrate for liquid crystal display panel preferably used as a color filter substrate of liquid crystal display device. More particularly, it relates to a substrate for liquid crystal display panel preferably used as a color filter substrate of liquid crystal display device in multidomain vertical alignment (MVA) mode and the like.
2. Description of the Related Art
The liquid crystal display device performs a display by controlling optical characteristics of light from a light source using a liquid crystal layer filled in a liquid crystal display panel, and the device is used in various fields because of its characteristics such as thin, light and low power consumption.
In general, a liquid crystal display panel which is a main member of such a liquid crystal display device has a structure in which a liquid crystal is sandwiched between a switching element array substrate and a color filter (CF) substrate and a thickness (cell gap) of a liquid crystal layer is maintained by a spacer arranged between the substrates. As the spacer, a sphere spacer formed of plastic or an inorganic material and the like and a columnar spacer formed of resin material and the like are known. It is preferable that the spacer is selectively arranged in a light shielding area (outside a display area) on a black matrix and the like so as not to lower display quality of the liquid crystal display device. In this respect, since the sphere spacer is spread so as to be arranged on a substrate in general, a high controlling technique is required in order to arrange it in a desired position. Meanwhile, the columnar spacer can be directly formed on a substrate by a photolithography method and the like using a photosensitive resin and the like. Therefore, it is superior in highly precise arrangement. In addition, the columnar spacer formed by such photolithography method is called a photo spacer (PS) also.
Conventionally, after the switching element array substrate and CF substrate are manufactured, the liquid crystal display panel is manufactured through a process of aligning, a process of bonding both substrates, a process of filling the liquid crystal and the like. In this case, the liquid crystal is filled by a vacuum injecting method. According to the vacuum injecting method, after both switching element array substrate and CF substrate are bonded, the bonded substrate is soaked in a liquid crystal bath and the liquid crystal is filled between the substrates by vacuum suction.
However, the liquid crystal display panel becomes larger recently and therefore the filling method of the liquid crystal is changed from the vacuum injecting method to a one drop filling method (a falling-drop method) in order to shorten the filling time of the liquid crystal. According to the one drop filling method, after the liquid crystal is dropped on one substrate (generally, on the CF substrate), the switching element array substrate and the CF substrate are bonded. Therefore, the liquid crystal can be filled in several minutes even in the case of a large-size liquid crystal display panel. Meanwhile, when the one drop filling method is used, it is necessary to strictly control an amount of the liquid crystal to be dropped in order to prevent an air bubble and the like in the liquid crystal layer. And when the liquid crystal is filled in the liquid crystal display panel having a projection structure such as PS, it is necessary to precisely measure a height and the like of the projection structure on the substrate to previously determine the amount of the liquid crystal to be dropped every cell.
As a method of measuring the height of the projection structure such as the PS without contacting a surface measured, a measuring technique using light interference (white light interference) is known, for example. When the height of the projection structure is automatically measured by the measuring technique using the while light interference, the most characteristic pattern (positioning part), distance data between the positioning part and a reference point (base point), and distance data between the positioning part and a top of the projection structure is previously set in a viewing range (measuring area) of an image recognition device. Thus, at the time of measurement, a measuring head is moved to the measuring area to perform rough origin setting (rough alignment) and then the positioning part is searched and precise origin setting is performed. Then, the top (coordinate) of the projection structure and the reference point are specified based on the above-mentioned distance data. Finally, the vicinity of the projection structure is irradiated with light from a white light source in a state in which an inclination angle is kept constant to form an interference stripe. And then height difference between the reference point and the top of the projection structure is measured by measuring a distance between the interference stripes.
When the PS height is automatically measured by such a measuring device, the positioning part for the origin setting by the measuring device has to exist on the substrate. However, when the projection structure on the substrate is used as the positioning part in case of the substrate for liquid crystal display panel, the positioning part could be confused with other patterns since many projection structures such as the columnar spacer and the protrusion for controlling an alignment are provided on the substrate. In addition, it is necessary to arrange the positioning part at a predetermined position precisely. When the PS (stacked PS) having a stacked structure is used as the positioning part, for example, the configuration of the interference stripe of the stacked PS formed by the white light interference is changed every measurement because of alignment shift of each layer, which causes a malfunction of the height measuring device. Thus, the substrate for liquid crystal display panel comprising a positioning part which can be appropriately used in origin setting by a measuring device has been demanded when PS height is measured.
In addition, the constitution of the columnar spacer is disclosed in many documents, for example, a CF substrate and the like in which a stacked PS is formed on a black matrix has been disclosed. However, there is no description about providing a positioning part used when the height of the columnar spacer is measured. Refer to Japanese Kokai Publication Hei-09-120063 (Patent Document 1), Japanese Kokai Publication Hei-10-232310 (Patent Document 2), Japanese Kokai Publication Hei-11-64618 (Patent Document 3), Japanese Kokai Publication Hei-11-248921 (Patent Document 4), Japanese Kokai Publication 2000-147234 (Patent Document 5), Japanese Kokai Publication No. 2000-258617 (Patent Document 6), Japanese Kokai Publication No. 2001-51266 (Patent Document 7), and Japanese Kokai Publication No. 2002-162629 (Patent Document 8), for example.
Regarding the positioning part provided on the substrate for liquid crystal display panel, it is disclosed that a positioning part used when the substrates are aligned at the time of bonding or a positioning part used in alignment of a mask at the time of forming a metal film pattern in a peripheral area of the substrate is arranged. However, there is room for improvement of a positioning part used in measuring PS height in view of its forming method and its arrangement. Refer to Japanese Kokai Publication No. Hei-09-127546 (Patent Document 9), Japanese Kokai Publication No. Hei-09-197434 (Patent Document 10), and Japanese Kokai Publication No. Hei-10-123549 (Patent Document 11), for example.